Running an Infinispan node in clustered mode using Testcontainers

In my last two blog posts I wrote about a library called Testcontainers. It’s a Java wrapper around docker containers and you can use it to run software that your application depends on in a test context. My last post presented a solution that makes it easier to start up an Infinispan caching server. This solution focused on a standalone Infinispan server. While this is probably good enough most of the time, sometimes you might need a server running in clustered mode. This post shows one solution for this.

Hotrod Topology State Transfer

I’ve been using the Hotrod protocol to connect clients to the server and if you’re running Infinispan in a cluster, clients will automatically be updated with new server addresses, each time a new node joins the cluster. This is called the Topology State Transfer and it also happens once initially. When you start a clustered Infinispan instance using Testcontainers (which is the default of the Docker hub Infinispan image), this means that the Infinispan node communicates its ip-address from inside the docker container to the client outside the container overwriting the previously configured connection information. I’ve covered this problem briefly in my last post. During the last week I’ve tried to find a way around this.

Configuring the Hotrod connector on the server

If you look at the default clustered configuration provided by Infinispan, you’ll find a section that configures the Hotrod connector.

It turns out you can adjust this configuration using two attributes: external-host and external-port. Hotrod will use the values of these attributes when communicating its address during the topology state transfer. While this sounds promising at first, there’s a problem: We can use localhost as a value for external-host but we don’t know, which port Docker will expose externally.

Ignoring the server updates on the client

If we can’t make the server behave differently, we can try to change the client and ignore the update. Let’s look at the error message:

We can see that the error message originates from a method called updateTopologyInfo in the TcpTransportFactory. Looking closer, we see the method updateServers() being called. Maybe we can create our own TcpTransportFactory that overrides this method and ignores the updated servers. I’ve updated the existing InfinispanContainer and created two sublcasses, so that we now have a StandaloneInfinispanContainer and a ClusteredInfinispanContainer. Both are subclasses of the InfinispanContainer base class. Here’s the custom TcpTransportFactory for the clustered container:

Our base container class configures the cache manager and uses the TcpTransportFactory provided by the subclass. If there’s none, the default behaviour will be used as before.

With this change in place, the server can now send the updated topology information – we don’t care anymore. For a complete picture, have a look at the git repository containing the complete code. Please tell me if you have comments or suggestions on how to improve my approach!